As nonvolatile storage elements in which no information is erased even when power is turned off, there have been proposed, for example, flash memories, Ferroelectric Random Access Memories (FeRAMs), Magnetoresistive Random Access Memories (MRAMs) and the like. In these storage elements, the written information can be continuously held for a long period of time even when power is not supplied. However, these storage elements have a problem. For example, flash memories have a high integration level, but have a low working speed. FeRAMs have a problem in the manufacturing process, and MRAMs have a problem in terms of their power consumption.
Accordingly, memory apparatuses having a new type of resistance change-type storage element have been developed. This storage element has a structure in which an ionic conductor containing a predetermined metal is disposed between two electrodes (for example, JP-A-2006-196537 and JP-A-2009-43757). In this storage element, atoms or ions are moved by heat or an electric field, and it is thought that the resistance value changes due to the formation of a conduction path.
In the data read-out from a memory cell having a plurality of the nonvolatile storage elements, a read-out circuit may be used to determine a state of the storage element, that is, determine whether the state is a written state or an erased state.